interactive pen-and-ink rendering for implicit...
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Interactive PenInteractive Pen--andand--Ink Rendering Ink Rendering for Implicit Surfacesfor Implicit Surfaces
Ryan SchmidtTobias Isenberg
Brian Wyvill
Introduction: Implicit SurfacesIntroduction: Implicit Surfaces
• many nice properties for shape modeling– CSG, blending, animation,
non-linear editing, …
• major drawback: visualization– finding the surface to render:
expensive!
– problematic for interactive editing
Implicit Surface VisualizationImplicit Surface Visualization
• ray-tracing– high quality but very slow
– off-line only
• polygonization– coarse meshes interactively
[Schmidt et al. 2005]
– refinement expensive
cour
tesy
of E
rwin
de
Gro
ot
What about NPR?What about NPR?
• non-photorealistic rendering– render “important” parts of the surface
– less geometry → potentially faster
• pen-and-ink [Foster et al. 2005]
• excellent results but still slow– ray-tracing
– surface-particle walks, etc.
from
[Fos
ter e
t al.
2005
], us
ed w
ith p
erm
issi
on
Basic Idea of Our ApproachBasic Idea of Our Approachfor Fast Rendering of Implicit Surfacesfor Fast Rendering of Implicit Surfaces
• use simplicity of polygonal NPR methods
• mesh provides sampling of implicit surface
• speed gains from using simple meshes
• goals:– approximate technique
– high-quality rendering
– dynamic meshes
Fast Approximate Implicit SilhouettesFast Approximate Implicit Silhouettes
• use coarse base iso-mesh
• compute sub-polygonsilhouettes on that mesh[Hertzmann & Zorin 2000]
• project vertices to iso-surfaceusing field gradient
• adaptively refine silhouette
Fast Approximate Implicit SilhouettesFast Approximate Implicit Silhouettes
Silhouette PrecisionSilhouette Precision
• fairly coarse iso-meshusable ...
... as long as featuresare captured by it
Silhouette PrecisionSilhouette Precision
• high-res mesh silhouette vs. refined approximate silhouette of low-res mesh
Fast Approximate Implicit SilhouettesFast Approximate Implicit Silhouettes
• profit from simple mesh-based techniques
• fast for coarse meshes, even brute-force
• very few field evaluations necessary
Hidden Line RemovalHidden Line Removal
• previous techniques too slow or inaccurate– implicit surface ray-intersection: expensive
– filling z-buffer with coarse mesh: inaccurate
– particle/surfel technique [Foster et al. 2005]: slow
• distribute points on coarse mesh triangles
• project them to implicit surface
• render small tangent disk into z-buffer
Hidden Line RemovalHidden Line Removal
lo-res mesh
lo-res mesh HLR lo-res surfel disc HLR
Suggestive ContoursSuggestive Contours
• view-dependent non-silhouette feature lines
• radial curvature kr = 0 [DeCarlo et al. 2003]
• finite differences method w/o third derivatives
Surface StipplingSurface Stippling
• re-use surfel disks from HLR– k stipple points per disk
– illumination regions following [Foster et al. 2005]
Geometry HierarchyGeometry Hierarchy
• triangles → discs → stipple points
• visibility culling– at each level of hierarchy
– back-face & illumination culling
• dynamic geometry generation– expand hierarchy only when required
– minimizes setup time for dynamic surfaces
Example: Lines + StipplingExample: Lines + Stippling
Performance: VideoPerformance: Video
machine:1.6 GHz Centrino laptop
Video: Interactive SessionVideo: Interactive Session
ContributionsContributions
• fast & efficient approximate silhouette extraction for implicit surfaces
• extended to suggestive contours & stippling
• faster than extraction of detailed iso-surface
• application: interactive modeling
• also works for other surfaces (e.g., NURBS)
Thanks for your attention!Thanks for your attention!
Thanks to our funding providers:
download demo at:http://www.unknownroad.com/shapeshop/